Wednesday, 12 June 2019

Inside the Racal BCC425 Initiate Box

Just in case anyone was wondering what was in the Clansman Initiate Box, well heres a photo

As you can see, its really very simple inside. Probably the easiest bit of Clansman to repair!

Support our charity fundraising! -

Did I mention our charity walk?

Those of you who frequent this blog may also be aware of my other, seldom updated walking blog. Well, myself and Bob M1BBV are yet again taking on a rediculously long walk for charity!

Next month, we will walk 84 miles in just 3 days, to conquer the Hadrians Wall long distance path. This is to raise funds for Cancer Research UK.

If you like my blog, and if anything ive put in my ramblings has been helpful to you, why not consider saying thanks with a bit of sponsorship?

You can donate to our cause at our dedicated fundraising page here

Please help us hit our target and help find a cure for cancer!

I'll be adding the link to each blog post as well.

Monday, 10 June 2019

Up, Up and Away!

Ive finally got around to starting the work on fitting the ADS-B receiver system into a weatherproof housing for mast installation. I happened to obtain an ex-equipment outdoor unit housing, and realised I could repurpose it from its original job of line protection unit.

Ive used the same antenna, but with some blind grommets and silicone. Mounting the electronics took some thinking about to ensure good all round ventilation and airflow, and access to the SD card.

I need to get some better blanking plugs for the holes before it can go outdoors. and work out how im going to attach mast mounting brackets.

Ive also done the necessary repairs to the rescue box kite. This involved learning how to completely dismantle it in order to take off the wing fabric in order to attach the repair tape, and to fix the broken longeron.

Im now waiting for the tapes adhesive to cure and then can fold it back up again.

PRC344 low battery warning v.1.0 - 1st working

After a lot of fiddly work with these tiny 0603 sized SMT parts, and the retrofit of a standard 1/4w resistor to effect the required virtual ground, I now have the very first of the version 1.0 boards installed and tested in my PRC344.

Fiddly work - those black specks are the resistors!

The chosen resistors for Ra and Rb actually, in use, give an alarm threshold of 20.86v. Thats a little higher than I was aiming for, but not bad for fixed value 5% components.

Completed board

Insulated inside heat-shrink ready to install

The radio is now back together, tested on the variable bench PSU, and now sat monitoring North-East ICF on 270.050MHz, where there is some activity. Rather annoyingly, there is a dreadful sproggie from my PC right on that very frequency! So I have to move the radio quite a way clear of the computer.

I now need to let the radio drain down the battery until the alarm starts, and then check the battery voltage and the alarm function.

Sunday, 9 June 2019

Project Delays

Its been some time since I posted on here, mostly due to being worked like a dog on overtime, but also some big household projects needed working on, and also training yet again for a charity walk.

Ive revisited the PRC344 battery warning project today. I'd forgotten about the modification needed to the v.1 PCBs! This is because I was let down by a supplier and am still waiting for the 100k and above resistors.

Needing to get at least some of these v.1 boards completed and up running, I tested the circuit on breadboard again tonight using 10k range resistors instead, just to prove that it works that way, which it does. I also tested various combinations of Ra and Rb in the 1-10k range and found a couple of combinations that give a 20.2v cut-off (4k7 and 6k8) or 18.7v cut-off (3k9 and 6k8). I'll have to check the minimum terminal voltages of the batteries and decide which to fit. I think though that 1v/cell really is best as a maximum discharge, so the 20.2v values will probably be chosen.

This will allow me to get at least a few of the boards working, at least until I run out of 0603 10k resistors! But I should at least be able to demonstrate one! Then, when the rest of the resistors arrive, the remaining boards can be made up with either 10k or 100k series.

Its now however almost certain that I will redesign for a v.2 board using 0805 size parts, this will allow the use of a better voltage rated and higher value capacitor for the timing, but I will also add the duty cycle control diodes as well.

Ive also, since last posting, acquired a WW2 rescue box kite (as used with the famous 'Gibson Girl' lifeboat transmitter) which I have repaired and restored. I am now in the process of building an antenna connection and protection unit, which will drain wind static and protect against electrical discharge. Once that is done, it will be time to attach an antenna wire, fly the kite and load up the Clansman!

Wednesday, 20 March 2019

Fatal Flaws!

Another nasty realisation looks like it might be the death of the first version of the PRC344 battery warning module!

Yesterday it came to light that a further 100k resistor was required. Not a difficult thing to add in itself. But while shopping for the 4M7 resistors needed for the timing, and realising that they are rather expensive, a consideration of the alternative, that is going to a 10uF capacitor and dropping the resistor down to 470k, led to the discovery that the 1uF ceramic capacitors im using are only rated at 16V!

I really dont know how far I could safely push that rating! A quick test shows that the voltage on the capacitor peaks at about 16V for a 24V supply. But, a freshly charged battery could easily be up to near 28V! And there are also single use 33V Lithium batteries out there! A check at 28V showed the capacitor to have over 19V on it!

There are 10uF 35V SMD tantalum capacitors available at good prices, but these are considerably bigger than the 1uF 0603 ceramic! No chance of a retro-fit mod here!

So, although I have a fair bit of cash tied up in the parts stock for these v.1 modules, it is looking risky to sell them as capable of being reliable in a 24V Clansman system. One option might be to add a potential divider on the supply line to keep the voltages safe of course! I will test that out. The whole module takes only a couple of mA so it should be a safe method, if a little untidy.

But another issue is that a non 50/50 duty cycle is preferred, and to do that requires extra parts anyway. I will test this out on breadboard, but whether I then invest in a v.2 module for sale will have to depend on if there is likely to be enough demand. I am also however going to test out whether or not I can do away with the switching transistor.

So the v.1 warning module looks like it might be a bit of a hybrid SMT/through hole unit, with fixed 3sec on/3sec off warning. This would at least save the project!

Touchy circuits!

Having received the LM358s, I set about checking the circuit for the PRC344 battery warning would behave as required on the breadboard.

Working now with just a single 8-pin DIL device meant that much of the circuit was scrunched up on the breadboard, making it tricky to see if everything was connected properly, so it was no surprise when it didnt bloody work!

After some time fiddling and testing, I discovered that the battery level detector side of the circuit did work just fine, but the astable multivibrator side didnt!

This now was where it got strange! The astable would work, but only if I had the tip of the multimeter probe touching pin5! Or, even weirder, if I myself touched pin5 or the leg of the resistor connected to it!

I checked everything! I tried different positions on the breadboard, different feedback resistors, battery supply, capacitors bypassing the pin to ground, capacitors bypassing supply to ground, even THREE different ICs! The damn thing just would NOT work unless I touched it!

By now, I was starting to think the worst! Ive got around £20 of PCBs and components tied up in this! What the heck can be wrong? Are the ICs junk?

No. It turns out, with thanks to MrBungle on the UK Vintage Radio Repair and Restoration forum who pointed this out to me, that pin5 in this case requires a 'virtual ground', made up of the two feedback resistors I had, plus another to the supply rail! I nipped out and added another 100k resistor, and lo and behold the bugger is oscillating again!

This means of course that my shiny PCBs are already out of spec and need modding! But, an additional resistor is hardly a big mod and wont make much difference to the space requirements. One aspect of this though is that the circuit now operates correctly, which it seems it wasnt doing with the 741 op-amp, and gives a 50/50 3sec duty cycle. Making it now do the 10sec off/2sec on that I previously had, requires even more modification, with the addition of at least another resistor and a diode, most likely two diodes. I can of course do this on the existing run of PCBs but its going to start getting a bit messy! If the board does prove to have some demand for it, then a mkII version will have to be made with the extra parts.

For now, im just glad that the damn circuit does in fact work! And yes, the big problem of the optocoupler being always slightly on has been solved by using the LM358!

Tuesday, 19 March 2019

Dual Dual Op-Amps!

The LM358 dual op-amps finally arrived today - both types! So I now have oodles of both DIL-8 and SOIC-8 dual op-amps to play with!

The first three of the battery warning modules now have their IC mounted. Im still waiting for the higher value 0603 chip resistors though, so cannot complete and test them just yet.

What I can do though now is rejig the breadboard prototype with an LM358 and test the system on that, which will allow me to find the most appropriate values for the sense resistors RA and RB. I do expect the values to be a little different than the LM741 circuit, but the biggest variation will be down to which of the standard values gives the closest threshold to the desired 20V.

Some of you reading this may also be aware of the sad passing of Rev George Dobbs G3RJV recently. The G-QRP club have set up a tribute fund on behalf of the Alzheimers Society, if you wish to make a donation

Monday, 18 March 2019

Any RF port in a storm

Although I havent been very active on air for a while, I have been running my U3S WSPR beacon on 40m. This had to stop over the weekend when the storm brought my HF doublet down. As I was working, it had to wait for today for repair. Nothing I like more than trying to make a decent Western Union splice stood atop step ladders! I am now repaired and back on air, although I havent yet had time to check the matching to see if the repair has affected anything. WSPR results since the repair seem ok.

With thanks to Alan G8LIT, my Clansman PRC344 is now housed neatly in its own 58 pattern carrier satchel, which cleaned up nicely with a bit of 'chelating mixture' (that is, flour and vinegar) on the metal work, and a spin through the wash.

Ive also acquired a vintage 2m multimode, from near the very start of the era! An FDK Multi-2000! This is a proper beast of a set, and has some rather curious features, such as its dial selected 10kHz steps, but with a +/- 7kHz VXO for FM! It weights a ton, mostly because it is a dual 12V DC/ 240VAC capable set.

Vintage FDK Multi-2000 2m multimode transceiver
Top View

Bottom View. Note homebrew pre-amp!

It does need some work doing though! The mains switch seems to work but the supply doesnt get from the switch to the regulator! I can power the set by connecting directly to the reservoir capacitor! The VXO doesnt seem to work, its a tad deaf, the output power is down, possibly due to a failed final transistor, a couple of the filament dial bulbs have blown, and the volume pot is noisy. There are also some joints in the internal wiring that have previously been taped and are now falling apart, but these go to the dial bulbs so i'll be replacing those anyway. Its also about 3kHz off frequency. Cosmetically its not bad for its age, theres a crack in the fascia but the knobs and front panel etc are all ok. Minor repair stuff really. Someone in the past has added a homebrew receive pre-amp as well.

One good thing about radios of this vintage is that the manuals came with the alignment details and circuit diagrams. So I have the manual, and will set about restoring it to usable condition. I dont think it will be too hard, most of the problems are very minor. My only real concern is the PA, getting a suitable replacement final transistor might be a challenge. I suspect the receiver can be brought up a bit just from alignment, but its possible that parts will be needed in the front end, or maybe even that homebrew pre-amp! Those big electrolytics might be a bit suspect as well after all these years!

The switching transistors for the battery warning modules came today, so my first three units now have that fitted. I do hope the rest of the parts dont take too long to arrive now!

Thursday, 14 March 2019

Prototype PCBs

Well, I have to say, im rather impressed!

I have been using the online EasyEDA to design the PCB layouts for the various Clansman projects im working on. Now, as much as I dislike the way EDA software uses device package symbols that bear little relation to how I was taught to lay out a schematic, you cant deny that the advantage of being able to let the software design the circuit boards takes a lot of the hard work of prototype design out. But what has impressed me is something that I can be forgiven for being skeptical of - that EasyEDA is 'tied in' with a Far East supplier of PCBs and components.

Having designed the SMD PCB for the PRC344 battery warning circuit, I decided I would take advantage of the offer of 10 PCBs for just $2 (about £1.60), to see how they came out.

I did make a bit of a mistake by not spotting which shipping service was selected, and got an invoice for well over £20! But having corrected that, I decided that the cheaper shipping, which brought the total up to £6, was still worth the risk. The first thing that raised an eyebrow was the near flawless tracking - the entire process was tracked! But even more surprising was being told the boards were etched and ready to ship just 2 days later!

They took about a week to arrive, which really isnt bad at all from China! And, as it turned out, most of the delay was by Royal Mail! And I have to say, they do look pretty good

Due to their very small size, the silkscreen print is rather limited, and given a choice I personally would have made some of the track a little wider ( I could have done that, but had no reference from which to decide how much thicker to go from the default).

Next step of course is to make one up and test it. Unfortunately, I am still awaiting delivery of several components, not least the LM358 op-amp that is at the heart of the circuit!

I gather that the low cost offer for 10x PCBs holds for boards up to 100mm x 100mm! My boards are about 15mm x 25mm! If I could just find a way to layout SMT parts on both sides of the PCB, I could create some amazingly compact circuits!

But, there are difficulties! To make these boards fit in the only safe available space in the PRC344, I had to choose 0603 sized parts. These are damn small! And to attach them to the board im using solder paste out of a tub! This is a new idea to me - in the past whenever ive had to rework SMT, ive had access to solder paste in dispensing syringes and a controlled pump, plus hot air reflow equipment. Here, im having to apply the paste with the tip of a probe, and then melt it with the tip of my soldering iron. Add on the fact that I dont have access to the high power magnification I used to use either, and it all makes for a rather tricky job!

But, that said, ive made a start. Im making three up at the moment, one is for my '344, the other two for further test and evaluation.

Fitting the miniMELF zener

The Zener diode is a miniMELF package. These are tricky buggers, as they are little cylinders and apt to roll off! As the only parts that I currently have stocked are the zener, opto and capacitor, these are the only parts ive been able to install just now. The capacitor is just about visible in the photo below!

zener, 1uF capacitor and optocoupler installed
 Each was then tested for continuity to ensure there were no shorts underneath! Once completed and tested, then connecting wires will be measured and attached, and the whole board housed in a length of heatshrink tubing. As nice as it is to be able to see the electronics, putting it into heatshrink will ensure it cannot cause any problems inside the radio!

As this design uses fixed resistors to save complexity and cost, its likely that a little compromise will be needed as to the exact threshold voltage at which the warning is activated. I'll aim to make this as close to 20v as I can, but it depends on where the standard resistor values come out. If I cant make it close enough with standard values, then one option is to parallel standard values by mounting them on top of each other! All that can be determined though using standard through hole parts on the breadboard once the DIL LM358s arrive! Of course, if I decide to offer some of these as kits, then the buyer can experiment as they see fit with the values of RA and RB, likewise, if they are not happy with the duty cycle of the alarm, they can play with other values as they wish.